1. Field of the Invention
This invention relates to cold plates for cooling electronics.
2. Description of the Related Art
Certain electronic devices generate heat as they operate, and in some cases this heat has to be removed or dissipated for the device to continue operating properly. Several techniques have been used to cool electronic equipment. Examples include fans, which are used to blow air over electronic equipment. This air serves to convectively cool the electronic equipment with normal ambient air. Other techniques that have been used include liquid cold plates. Liquid cold plates are plates with channels through which liquid flows. The electronic equipment is mounted in contact with a liquid cold plate and the heat generated by the electronic equipment is transferred to the liquid coolant inside the cold plate. This can provide better cooling than the convective cooling provided by a fan with considerably less flow volume. It can also provide better temperature consistency with less acoustic noise.
Cold plates can be directly affixed to a heat-producing piece of electronic equipment, such as an electronic chip or an insulated gated bipolar transistor (IGBT). It is also possible to use thermal grease or other heat transfer aid between the electronic equipment and the cold plate to improve heat transfer. Typically, the cold plate includes an inlet and an outlet for liquid coolant flow. The liquid coolant absorbs the heat produced by the electronic equipment, and transfers the absorbed heat to the coolant which then flows out of the cold plate. Many cold plates provide cooling with a relatively low flow of liquid coolant. They can provide better temperature consistency than convective cooling, minimal acoustic noise and the cooling power of liquid coolants.
Several factors impact the performance and desirability of cold plates, and different factors are important for different uses. Some important factors include cost of production and ease of producing relatively large quantities. Cooling efficiency should be high, and cold plates should be securely sealed to prevent any leak of liquid coolant onto the electronic equipment being cooled.
In some applications, the coolant may not be particularly clean, which can result in plugging of the cold plate. For example, a cold plate used in an automobile may utilize the anti-freeze liquid for cooling, and the anti-freeze can contain small particulates. In other applications, there may be a phase transfer within a cold plate to help facilitate cooling. It is also possible for a cold plate to be used for heating a component by replacing the coolant with a heating fluid. One primary difference between a coolant and a heating fluid in one phase heat transfer is that the temperature of a coolant is lower than the item being cooled, and the temperature of a heating fluid is higher than the item being heated.
Many different techniques are used to cool electronic components, and new techniques which provide cooling benefits are desirable. Thermal control can be important for the operation of cold plates, but thermal control can also be used in the manufacturing of electronic components, such as soldering electronic connections. Various contact points on an electronic component often must be soldered for reliable electrical contact. In some cases, it is preferable or even necessary to complete the soldering of electronic components after they have been connected to a cold plate.
Known soldering processes include the flow solder method wherein already liquid solder is applied to the soldering area, and several reflow soldering methods wherein solid solder is applied to the parts and melted to produce the soldered joint. Examples of such reflow soldering methods are infrared soldering, wherein the melting of the solder is carried out by means of infrared radiation; hot bar soldering, wherein the heat transfer is carried out through contact with a heated bar; hot-air soldering, wherein the heat transfer is carried out by convection; and vapor-phase soldering, wherein the heat transfer is carried out by condensation of the vapor in the area to be soldered.
When using these known soldering processes, a thermal overloading of the parts to be soldered can occur. Thermal overload can be minimized by keeping the temperatures of the parts to be soldered as low as possible, i.e. just above the melting point of the solder. During several established soldering processes, there can be a temperature difference of 30 degree Centigrade or more between the temperature of the heat transfer medium and the melting point of the solder. This temperature difference may help the soldering process with adequate heat transfer during the time interval needed for manufacture of the components. Some of the mentioned processes are not conducive to exact temperature control during the soldering process, and minor temperature adjustments during the heat transfer process may be difficult or impossible.